Before the real work can begin on a replacement for New York State's Tappan Zee Bridge, crews need to construct a jobsite. The $3.9-billion design-build project has limited access on both sides of the river, so workers are erecting massive steel trestles that will serve as staging areas.
By the time permanent foundation piles are driven in October, this three-mile-wide stretch of the Hudson River, about 20 miles upstream from New York City, will be a bustling jobsite. Two steel trestles—1,300 ft long and 1,040 ft long, respectively—will line its shores, and up to 100 barges with as many as 30 cranes will be working concurrently in the river.
"The main construction at this time is the temporary trestle on the Westchester side of the river," says Walter Reichert, vice president and project manager with the design-build contractor Tappan Zee Constructors. TZ Constructors is an LLC composed of American Bridge, Fluor, Granite Construction and Traylor Bros., with HDR serving as design partner.
"The location of this project is the real challenge," says Reichert. "We are working very close to a community that is sensitive to the building process." There have been only two noise complaints so far, and TZ Constructors limits the hours of pile-driving to midday weekdays. Multiple environmental monitors have been installed on both shores, with data viewable online to the public.
TZ Constructors' design calls for 964 foundation piles and approximately one million cubic yards of dredging. The project's environmental impact statement does not allow for dredging up to the shoreline, hence the need for the trestles.
Shoreline access is limited on the western Rockland County side and almost nonexistent on the eastern Westchester County side. TZ Constructors is in negotiations to rent a dock a few miles away on the Hudson River. There, heavy equipment and materials can be delivered and loaded onto barges for transport to the site, says Brian Conybeare, spokesman and special adviser to the governor for the New N.Y. Bridge project.
"Preconstruction is well under way on this project, and you're going to see it ramp up in the next several months," says Conybeare. "River-based test borings are complete, and test pile drivings are going to begin in late June, early July."
Unlike the existing Tappan Zee Bridge's concrete caissons, most of the new bridge's pilings will be anchored in bedrock. Approximately 30% of them will be friction piles driven into the muck of the Hudson River. They will be located in a section of the span's western approach, where the soil conditions are known to be very poor, with significant sloping in the substrate.
Procurement will begin in mid- to late summer, says TZ Constructors' Reichert. Dredging won't begin until August, notes Conybeare, as outlined in the project's EIS. "We're only allowed to dredge from August 1 to November 1 to protect the endangered species in the river, the Atlantic and short-nosed sturgeon. That window avoids their main spawning and migration season," he says.